Process for enhanced oil recovery from subterranean formations

Abstract

A method for recovering hydrocarbons from a subterranean hydrocarbon bearing formation comprises the steps of providing a production well penetrating in the formation and a plurality of injection wells surrounding the production well. Water is injected into the formation through the injection wells to produce a water flood barrier ringing the production well. A mixture of nitrogen and carbon dioxide gas is injected through the production well and into the formation with the water barrier acting to inhibit the escape of the gas from the portion of the formation surrounding the production well. Gas is injected through the production well into the formation until the formation is pressurized and then gas injection is ceased and the mixture of hydrocarbons and injection gas flowed from the formation through the production well.

What is claimed and desired by Letters Patent is as follows: 
     
       1. A method for recovering hydrocarbons from a subterranean hydrocarbon-bearing formation comprising the steps of: (a) providing a production well penetrating into said formation;   (b) providing a plurality of injection wells surrounding said production well and penetrating into said formation;   (c) injecting water through said injection wells into said formation and substantially continuously water flooding said formation toward said production well;   (d) substantially simultaneously with injecting said water through said injection wells, injecting a mixture of nitrogen and carbon dioxide gas through said production well and into said formation with said water providing a barrier to escape of said gas from a portion of said formation surrounding said production well;   (e) continuing injection of said gas through said production well into said formation and pressurizing said portion of said formation;   (f) ceasing injection of said gas through said production well and flowing said hydrocarbons from said formation.   
     
     
       2. The method set forth in claim 1 wherein: (a) said gas is approximately 87-88 percent nitrogen and 12-13 percent carbon dioxide.   
     
     
       3. The method set forth in claim 2 including: (a) providing an internal combustion engine;   (b) operating said engine at a very rich mixture setting to provide said gas as an exhaust gas;   (c) routing said gas to said production well.   
     
     
       4. The method set forth in claim 1 wherein: (a) said gas is injected into said production well at a pressure of one-half to one pound per foot of depth of said production well to said formation.   
     
     
       5. The method set forth in claim 1 wherein: (a) said water is injected into said injection wells at a rate of about 10 to 30 barrels per day per well.   
     
     
       6. A method of recovering hydrocarbons from a subterranean hydrocarbon-bearing formation comprising the steps of: (a) providing a production well penetrating into said formation;   (b) providing a plurality of injection wells surrounding said production well and penetrating into said formation;   (c) injecting water through said injection wells into said formation and substantially continuously water flooding said formation toward said production well;   (d) providing an internal combustion engine emitting exhaust gas comprising a mixture of about 87 to 88 percent nitrogen and 12 to 13 percent carbon dioxide and routing said gas into said production well;   (e) substantially simultaneously with injecting said water through said injection wells, injecting said gas through said production well into said formation with said water providing a barrier against escape of said gas from a portion of said formation surrounding said production well;   (f) continuing injection of said gas through said production well into said formation and pressurizing said formation to a pressure of one-half to one pound per foot of depth of said production well to said formation;   (g) ceasing injection of said gas through said production well; and   (h) pumping said hydrocarbons through said production well from said formation.